Continuous process for producing acrylic esters

ABSTRACT

IN A PROCESS FOR PRODUCING ALKYL ACRYLATES FROM ACRYLIC ACID AND ALKYL SULFATES OR ALKYL ARYLSULFONATES, THE CONTINUOUS PROCESS IN WHICH THE REACTANTS ARE PASSED THROUGH A PIPE REACTOR IN A RESIDENCE TIME OF 10 SECONDS TO 20 MINUTES AND ALLOWED TO REACT IN LIQUID PHASE AT A TEMPERATURE OF 150*C. TO 220*C. UNDER A PRESSURE OF 2 KG./CM.2 TO 15 KG./CM.2 (GAUGE) TO OBTAIN THE ALKYL ACRYLATES IN HIGH CONVERSION WITH GOOD SELECTIVITY.

A ril27, r NAQYA KQMINAMI E TAL I 3,576,850

- CONTINUOUS PROCESS FOR PRODUCING ACRYLIC ESTERS Filed May 23, 1969 z 6 m F F 6 WW 4 W n L W m w w w w DISTRH/T/O/V R4770 OF RES/DENCE TIME United States Patent US. Cl. 260-486 4 Claims ABSTRACT OF THE DISCLOSURE In a process for producing alkyl acrylates from acrylic acid and alkyl sulfates or alkyl arylsulfonates, the continuous process in which the reactants are passed through a pipe reactor in a residence time of seconds to minutes and allowed to react in liquid phase at a temperature of 150 C. to 220 C. under a pressure of 2 kg./cm. to 15 kg./cm. (gauge) to obtain the alkyl acrylates in high conversion with good selectivity.

The present invention relates to a process for producing continously alkyl acrylates from acrylic acid and alkyl sulfates or alkyl arylsulfonates.

As the process for producing acrylic esters, so-called Reppes carbonyl reaction has been hitherto known, in which acetylene, carbon monoxides and an alcohol are allowed to react under pressure. In addition, the process for obtaining the same by esterification of acrylic acid with alcohols has been widely known. However, these processes do not belong to so-called petroleum chemical industry in the point of the use of acetylene and/or an alcohol, and actually the production costs too much according thereto.

Recently, two processes have been proposed, one of which relates to a process for producing ethyl acrylate by reacting at 70 C. in the presence of a small amount of water acrylic acid with diethyl sulfate which are obtained by absorbing ethylene into sulfuric acid (Japanese patent publication No. 2689/66), and another of *which is a process for producing the same by reacting acrylic acid with diethylsulfate at a temperature of 90 C. in the presence of monoethyl sulfate (French Pat. No. 1,488,- 022). However, both processes have the following drawbacks in commercial practice, due to their batch reaction using tank reactor at lower temperature.

(1) Necessitation of a long residence time for obtaining high conversion.

(2) Restriction to reactor utilizable for continuous process due to the above drawback (l).

(3) Low space time yield or low performance.

Accordingly, it is hard to say that they are always satisfactory for large scale production.

The object of the present invention is to provide a continuous process for producing alkyl acrylates adoptable in large scale production in high conversion with good selectivity from acrylic acid and alkyl sulfates or alkyl arylsulfonates.

The object is achieved according to the present invention which relates to a process for producing alkyl acrylate continuously comprising reacting in liquid phase acrylic acid with alkyl sulfates or alkyl arylsulfonates by passing through a pipe reactor in a residence time of 10 seconds to 20 minutes, at a temperature of 150 to 220 C. under a pressure of 2 to 15 kg./cm. (gauge).

The inventors have found from their studies that in the reaction of acrylic acid and alkyl esters such as alkyl sulfates the reactants and reaction products tend to polym ice erize quite easily to form oligomers and polymers as by products, and that this causes the yield of the objective acrylates lower. The tendency is greater especially in the continuous process using, for example, tank reactors, rendering the yield of acrylates extremely lower.

After further studies on the continuous process, the inventors have found that the continuous reaction of acrylic acid and alkyl sulfates or alkyl arylsulfonates can be con ducted with good yield of acrylates in a pipe reactor by selecting a limited residence time, and further that according to such process the reaction proceeds at a temperature sufiiciently higher than in the conventional processes, and thus acrylates are obtained in good yield at remarkably higher reaction rate as compared with that in the reaction at a lower temperature of the conventional processes. The present invention is based on the above findings.

A feature of the present invention resides in that acrylates are produced in high conversion of acrylic acid with good selectivity of acrylates on the converted acrylic acid, despite that it has been hitherto believed that acrylates could not be obtained at all in good yield in such reaction at high temperature, because alkyl sulfates would decompose and the polymerization rates of the reactants and products would be accelerated.

The present invention will be more particularly explained in the following description.

It has been found that in the reaction between acrylic acid and diethyl sulfate as an alkyl sulfate to form ethyl acrylate, the higher the conversion of acrylic acid is attempted or the higher the reaction temperature is adopted, the lower the yield or selectivity of acrylates becomes. The reason of such lowering the selectivity lies in the formation of oligomers and polymers above mentioned. In the oligomers and polymers there have been found the polymerized materials of ethyl acrylate, acrylic acid and ethylene. Thus, it has been found that the lowering of yield are caused by the side reaction in which the starting materials of acrylic acid and diethyl sulfate as well as the reaction product of ethyl acrylate are subjected to polymerization during such reaction.

Thus, the attempt to improve the conversion accompanies certainly the lowering of selectivity, and it has believed very difficult to maintain the high conversion together with the high selectivity. The inventors have considered the cause and come to the conclusion that besides the optimum reaction temperature and optimum reaction time there would be another requisite to correlate the effects of the above conditions to the improvement of the selectivity in the reaction.

When considering individual molecules in reaction and production systems, optimum temperature and optimum residence time whereby the reaction is conducted, would be definite in case of the reaction of 1 mol of acrylic acid and 1 mol of diethyl sulfate to form 1 mol of ethyl acrylate, and the starting materials as well as the reaction products are subjected to side-reaction resulting in no formation of the objective ethyl acrylate if the reaction is conducted with deviating from the optimum conditions. However, in effecting the reaction in continuously practising industrial scale all of the molecules are not always under the optimum conditions which are established from the point of view for rendering the continuous reaction feasible in high conversion, but deviate therefrom thereby there exist certainly the molecules which cause the side reaction, resulting in the lowering of the selectivity when considering the whole system. Accordingly, when the optimum temperature is established the more the molecules subjected to the optimum residence time are, in other words, the sharper the residence time distribution as shown in FIG. 1 is, the higher the selectivity would be.

From the point of view, it has been believed that the Patented Apr. 27, 1971 principal requisite influencing the effects of the conditions lies in the manner of conduction of the reaction under the condition rendering the residence time distribution sharp, that is, under such a condition that enables the most possible molecules to be in the optimum residence time, among various conditions improving the selectivity. The present invention provides a concrete means for such condition. In selecting the concrete means, it has been previously studied how much sharpness of the residence time distribution is necessary for feasibility of the industrial scale process. It has been known that when a continuous reaction is eifected in various shaped reactors the residence time distribution alters generally due to the shape of the reactor used, even though the average residence time is same in each other.

As the typical example, the comparison of the residence time distribution in tank reactor and pipe reactor is shown in FIG. 1 wherein curves (a), (b) and (c) are plotted in cases of a tank reactor, a pipe reactor with (i and a pipe reactor with (i which is less than a respectively, and symbols therein are as follows:

=average residence time 0=residence time E() :amount of a fluid effluent from the outlet of the reactor after hours since the same was pulsed in the in-let of the reactor when equals to zero.

The total efiiuent is assumed to be represented by the formula From FIG. 1, it is clear that the curves of residence time distribution in pipe reactors are quite sharp and different as compared with that in tank reactor. At the sacrifice of simplifying the apparatus, continuity of reaction or workability of operation, a reactor having considerably sharp residence time distribution curve would be selectable. In the reaction of the present invention, there occurs that the selectivity around 80% can be naturally attained in a continuous process conducted at a higher conversion rate even with a residence time distribution lacking for more or less sharpness. In view of this matter, and other requisites, such as simpleness of apparatus, workability of operation, a pipe reactor is selected in the present invention as a reactor having considerably sharp residence time distribution, simple construction, meeting, other requisites and enabling to maintain the selectivity around 80% within a wide range of temperature and residence time. The preferable pipe reactor used according to the present invention is one having a ratio of length to inside diameter (hereinafter referred to l/d) of above 10. A pipe reactor having a plurality of pipes may also be used.

The knowledge above mentioned is demonstrated in FIG. 2 which shows the relation between the selectivity of acrylate produced and the residence time distribution or sharpness thereof. In the figure, residence time distribution ratio is represented by the formula Residence time distribution ratio: 00

j, E d

wherein E() and q5 are same as defined above, and each number with percent in parentheses is the conversion of acrylic acid in examples and comparative examples hereinafter illustrated, which are shown as follows 4 (5) Example 5 using a pipe reactor (I.D.=3 mm.,

(6) Example 6 using a pipe reactor (I.D.=9 mm.,

l=500 mm.)

(7) Example 7 using a pipe reactor (I.D.=16 mm.,

*LD. represents inside diameter and Z represents length of the pipe reactor.

The residence time distribution ratio showsthe sharpness of the residence time distribution. That is, the more the proportion of molecules, among the whole reacted molecules, is included in average residence time of :25 percent when equals 1 (this shows that almost all molecules are under a residence time same as average residence time), the higher the selectivity of ethyl acrylate becomes. The figure shows that when the ratio is below 40 percent, the selectivity decreases abruptly. The selectivity of ethyl acrylate according to the process of the present invention is high in all cases because of sharpness of the residence time distribution.

The range of residence time taken for determining the residence time distribution ratio in FIG. 2 was set up to be i-2S% of the average residence time therearound on the basis that, due to the fact that the residence time distribution is continuous around the average residence time, the molecules residing in the range of i25% around the average residence time i.e., in the range of 50% of the Whole residence time are considered to represent the principal aspect of the total molecules.

It is appreciated from the figure that the high yield obtained according to the process of the present invention is based on the ground of the aforementioned mechanism. The same mechanism has been confirmed in the reaction of acrylic acid and other alkyl sulfates or alkyl arylsulfonates.

The process according to the present invention is superior to the conventional processes in the following points.

(1) The reaction can be effected continuously while maintaining high yield.

(2) The reaction rate increases ten-fold as much as that of the conventional processes, and the space time yield also increases as much as ten-fold.

(3) High conversion can be achieved, and thereby the amount of recycles such as easily polymerizable or decomposable unreacted acrylic acid and alkyl sulfates are much decreased, resulting in simplifying the purifying steps.

(4) High selectivity at high conversion can be achieved due to adopting high reaction temperature in a pipe reactor.

Thus, it will be appreciated that the present invention is a new industrial continuous process for producing acrylates in which the drawbacks inherent in conventional processes are all eliminated.

The reaction temperature used in the process according to the present invention lies in the range of to 220 C., and preferably to C. At a temperature below 150 C., the reaction rate becomes small, and this necessitates a long residence time, inviting dull residence time distribution. On the other hand, at a high temperature above 220 C., the polymerization or decomposition of the starting materials and reaction products increase, and this invites lowering of the selectivity. The residence time is taken in a range of 10 seconds to 20 minutes inclusively, and preferably 30 seconds to 10 minutes, and in such short time high yield at high conversion can be achieved.

The pressure used in the process of the present invention is in the range between 2 and 15 kg./cm. (gauge) which is autogeneous pressure of the reactants and products in the reactor at the temperature used.

The esterificating agent used in the present process includes alkyl sulfates of 2 to 4 carbon atoms such as ethyl sulfates, propyl sulfates, and butyl sulfates, or alkyl arylsulfonates having alkyl group of 2 to 4 carbon atoms and aryl group of 6 to 8 carbon atoms, such as ethyl benzenesulfonate, propyl benzenesulfonates, butyl benzenesulfonates and ethyl toluenesulfonates, which sulfates and arylsulfonates are obtained by absorbing olefins such as ethylene, propylene and butylenes into sulfuric acid and arylsulfonic acids, respectively.

The proportion of the esten'ficating agent to acrylic acid is preferably in above 1:1 by gram equivalent ratio, that is, excess of esterificating agent.

In the process according to the present invention, a solvent such as tetrachlorocarbon and cyclohexane may be added to the starting materials.

Furthermore, the present process is preferably practised in the presence of polymerization inhibitors in which suitable ones include hydroquinone, hydroquinone monomethyl ether, phenol and cresols.

The present invention is illustrated more particularly by the following examples which are not intended to limit the scope of the invention defined in the claims.

EXAMPLE 1 A reactant mixture of acrylic acid containing 0.7 percent by weight of hydroquinone and diethyl sulfate in a proportion of 122.14 by weight was continuously reacted in liquid phase in a pipe reactor having an inside diameter of 3 mm. and a length of l m., connected with a pump for supplying the mixture and a reservoir for the reaction product, under the condition of a temperature of 180 C., a pressure of l 'g./cm. (gauge), a supplying ratio of 3.8 ml./ min. and a residence time of 1.9 minutes.

Samples of the reaction product were successively taken out from a sampling out-let situated at the out-let of the reactor and analysed.

The analysis of the samples at a stationary state showed that the reaction was conducted in an acrylic acid conversion of 77 prcent, ethyl acrylate selectivity of 86 percent based on the converted acrylic acid and 94 percent on diethyl sulfate, respectively.

COMPARATIVE EXAMPLE 1 A mixture of 154 parts by weight of diethyl sulfate, 72 parts by weight of acrylic acid and 0.5 part by weight of hydroquinone was charged in a 200 ml. autoclave provided with a stirrer, thermometer, heating jacket and inlet and out-let valves for the material and reaction product, respectively. The autoclave was given a pressure of 5 kg./cm. (gauge) with nitrogen, and the content thereof was heated to 180 C. while stirring. At that temperature, reaction was conducted in such a way that a mixture of acrylic acid containing 0.7 percent by weight of hydroquinone and diethyl sulfate in a proportion of 1:2.14 by weight was introduced continuously from the in-let at a rate of 57 ml./ min. and in a residence time of 1.9 minutes, and simultaneously the same amounts of reaction product were discharged continuously from the out-let.

Samples of the discharged reaction product were taken out successively and analysed. The analysis of the samples at a stationary state showed such a result of the reaction that the conversion of acrylic acid was 62 percent and, the selectivity of ethyl acrylate was 54 percent on the converted acrylic acid and 57 percent on the diethyl sulfate, respectively.

EXAMPLE 2 Using the reaction equipment as described in Example 1, a continuous reaction was conducted at a temperature of 170 C., in a residence time of 2.8 minutes under a pressure of 4 'kg./crn. (gauge) by the use of a mixture of acrylic acid and dipropyl sulfate in a proportion of 1:2.53 by weight.

As the result, an acrylic acid conversion of 73 percent and a selectivity of 89 percent of propyl acrylate on the converted acrylic acid were obtained.

6 COMPARATIVE EXAMPLE 2 182 parts by weight of dipropyl sulfate and 72 parts of acrylic acid containing 0.7 percent by weight of hydroquinone were charged in the autoclave as described in Comparative Example 1. The autoclave was given a pressure of 4 l :g./cm. (gauge) with nitrogen, and heated at a temperature of 170 C. while stirring. At that temperature, reaction was conducted in such a way that a mixture of acrylic acid and dipropyl sulfate in a proportion of 1:253 by weight was introduced continuously from the in-let at a rate of the residence time of 2.8 minutes, while the same amounts of the reaction product were continuously discharged from the out-let.

The successive analysis of the discharged liquor showed that the conversion of acrylic acid was 57 percent and the selectivity of propyl acrylate was 59 percent on the converted acrylic acid.

EXAMPLE 3 Through a pipe reactor having an inside diameter of 3 mm. and a length of 3 m., connected with reservoirs for the reactants and reaction products and a pump for supplying the reactants, a reactant mixture of acrylic acid and diethyl sulfate in a molar proportion of 1:5 was continuously passed in a residence time of 0.7 minute and allowed to react in liquid phase at a temperature of 220 C. under a pressure of 14 kg./cm. (gauge).

The reaction product collected in the reservoir was successively taken and analysed. As the results, the conversion of acrylic acid was 70 percent and the selectivity of ethyl acrylate was 72 percent on the reacted acrylic acid.

EXAMPLE. 4

Through the reaction equipment as described in Example 3, a reactant mixture of acrylic acid and isobutyl benzenesulfonate in a molar proportion of 1:5 was continuously passed in a residence time of 10 minutes and allowed to react at a temperature of 150 C. The analysis of the reaction product showed that the conversion of acrylic acid was 82 percent and the selectivity of isobutyl acrylate was 84 percent on the reacted acrylic acid.

EXAMPLE 5 Through the reaction equipment as described in Example 3, a reactant mixture of acrylic acid and ethyl benzenesulfonate in a molar proportion of 1:10 was continuously passed in a residence time of 1.6 minutes and allowed to react at a temperature of 190 C. The analysis of the reaction product showed that the conversion of acrylic acid was 74 percent and the selectivity of ethyl acrylate was 95 percent on the reacted acrylic acid.

EXAMPLE 6 Through a pipe reactor having an inside diameter of 9 mm. and a length of 500 mm., connected with reservoirs for the reactants and reaction products and a pump for supplying the reactants, a reactant mixture of acrylic acid and diethyl sulfate in a molar proportion of 1:4 was continuously passed in a residence time of 2.4 minutes and allowed to react in liquid phase at a temperature of 180 C. under a pressure of 2 kg./cm. (gauge).

The reaction product collected in the reservoir was successively taken and subjected to analysis. The analysis showed that the converision of acrylic acid was 85 percent and the selectivity of ethyl acrylate was percent on the reacted acrylic acid.

EXAMPLE 7 Through a pipe reactor having an inside diameter of 16 mm. and a length of 190 mm., equipped as described in Example 6, a reaction mixture of acrylic acid containing 0.7 percent of hydroquinone and diethyl sulfate in a molar proportion of 1:4 was continuously passed in a residence time of 3.0 minutes and allowed to react in liquid phase at a reaction temperature of C. under a pressure of 2 kg./cm. (gauge). The analysis of samples taken successively from the out-let of the reactor showed that the conversion of acrylic acid was 89 percent and the selectivity of ethyl acrylate was 85 percent on the reacted acrylic acid, at the stationary state.

EXAMPLE 8 Through a pipe reactor having an inside diameter of 3 mm. and a length of 500 mm., connected with reactant reservoir, reaction product reservoir and pump for supplying reactants, a reactant mixture of acrylic acid containing 0.2 percent by weight of hydroquinone and dibutyl sulfate in a molar proportion of 1:2 was continuously passed in a residence time of 7.0 minutes and allowed to react in liquid phase at 160 C. under a pressure of 3 kg./cm. (gauge). The analysis of the reaction product showed that the conversion of acrylic acid was 78 percent and the selectivity of butyl acrylate was 85 percent on the converted acrylic acid.

EXAMPLE 9 Through a pipe reactor having an inside diameter of 2 mm. and a length of 3 m., equipped as described in Example 8, a reactant mixture of acrylic acid and ethyl xylenesulfonate in a molar proportion of 1:5 was continuously passed in a residence time of 0.5 minute and allowed to react in liquid phase at a temperature of 210 C. under a pressure of 12 l g./cm. (gauge).

The reaction product collected in the reservoir was successively analysed. As the result, the conversion of acrylic acid was 65 percent and the selectivity of ethyl acrylate was 89 percent on the converted acrylic acid.

EXAMPLE Through the reaction equipment as described in Example 9, a reactant mixture of acrylic acid and diethyl sulfate in a molar proportion of 1:2 was passed continuously in a residence time of 15 minutes and allowed to react in liquid phase at a temperature of 180 C. under a pressure of 2 kg./cm. (gauge).

The reaction product collected in the reservoir was successively analysed. As the result, the conversion of 8 acrylic acid amounted to 93 percent and the selectivity of ethyl acrylate was 67 percent.

EXAMPLE 11 Through the reaction equipment as described in Example 9, a reactant mixture of acrylic acid and ethyl benzenesulfonate in a molar proportion of 1:5 was passed continuously in a residence time of 4.5 minutes and allowed to react in liquid phase at a temperature of 170 C. under a pressure of 5 kg./cm. (gauge).

The reaction product in the reservoir was analysed successively. As the result, the conversion of acrylic acid was 83 percent and the selectivity of ethyl acrylate was 79 percent on the converted acrylic acid.

What is claimed is:

1. In a process for producing alkyl acrylate comprising reacting acrylic acid with alkyl sulfates or alkyl arylsulfonates having 2 to 4 carbon atoms in their one alkyl moiety and 6 to 8 carbon atoms in their one aryl moiety, the continuous process comprising reacting in liquid phase the both reactants by passing through a pipe reactor in a residence time of 10 seconds to 20 minutes, at a temperature of to 220 C. under a pressure of 2 to 1'5 kg./cm. (gauge).

2. A process according to claim 1 wherein the pipe reactor has a ratio of length to inside diameter of above 10.

3. A process according to claim 1 wherein the reaction is effected in the presence of a polymerization inhibitor.

4. A process according to claim 1 wherein the reaction is effected in the presence of a solvent.

References Cited UNITED STATES PATENTS 3,359,305 12/1967 Sheetz 260-486 3,392,191 7/1968 Ensor 260-486 LORRAINE A. WEINBERGER, Primary Examiner P. J. KILLOS, Assistant Examiner 

